Hexagon Key Hex Long Arm Ball End Wrench 1.5-19mm Allen Wrench L Shape Allen Key

Measure the width across the flat faces of the hex socket opening on your bolt — this is the key size you need. Common sizes for bicycles are 4mm, 5mm, and 6mm; furniture assembly typically uses 4mm or 5mm; larger machinery fasteners may require 8mm–19mm. When in doubt, a snug fit with no play is correct — a loose key will round out the socket.

A ball end tip allows you to insert the key at an angle (up to approximately 30° off-axis) rather than requiring a perfectly straight alignment. This is especially useful when a bolt is partially obstructed by a frame, panel, or adjacent component. Note: ball end engagement is best for moderate torque — for final tightening at full torque, use the straight short arm end.

These wrenches are sized in metric (mm) and are designed for metric hex socket fasteners. While some metric sizes are close to SAE equivalents, using a metric key on an SAE fastener (or vice versa) risks rounding the socket. Always confirm whether your fastener uses metric or SAE sizing before selecting a key.

Black oxide provides a degree of corrosion resistance and is suitable for typical indoor workshop and garage environments. It is not fully rust-proof under prolonged exposure to moisture or outdoor conditions. For extended tool life, wipe the wrench dry after use and store in a dry location. A light coat of tool oil can further protect the finish.

S2 tool steel hex keys are rated for the torque demands of standard metric fasteners within their size range. Smaller sizes (1.5mm–3mm) are suited for low-torque precision fasteners; larger sizes (8mm–19mm) can handle significantly higher torque loads. Avoid using extension pipes or excessive force beyond the natural leverage of the L-shape — this can damage both the key and the fastener.

Each size is sold separately, with pack quantities varying by size (1, 2, or 5 pieces per order depending on the variant selected). This lets you stock up on the sizes you use most without paying for sizes you don't need. Select your preferred size and quantity from the variant options above.

Most bicycle stem bolts, handlebar clamps, and brake calipers use 4mm, 5mm, or 6mm hex keys. Derailleur limit screws and some saddle clamps use 3mm or 4mm. Bottom bracket and crank bolts on some systems use 8mm or 10mm. Check your component manufacturer's specifications to confirm the exact size required.